The present invention relates to image scanning systems having AC illumination drives. It finds particular application in conjunction with a method and apparatus for eliminating lamp strobing in an optical scanning system, and will be described with particular reference thereto. It is to be appreciated, however, that the invention will also find application in conjunction with eliminating lamp strobing in a variety of image acquisition and output devices, such as scanners and xerographic copiers.
In imaging and scanning systems employing a time varying illumination source, there is the potential for process-direction nonuniformities to occur. More particularly, because the illuminator or lamp output fluctuates periodically in response to the lamp power supply, the summation or integration of lamp irradiance during a given scan line integration may vary from scan line to scan line, depending upon the time varying phase of the lamp power supply. Such a variation in integrated lamp irradiance from scan line to scan line causes image nonuniformities, such as strobing, i.e., varying degrees of image brightness between scan lines.
One solution to the strobing problem involves phase synchronization between the lamp power supply and the effective integration time. In other words, phase synchronization requires that the effective start of integration for each scan line occurs at the same relative phase in the lamp power supply oscillation. In this case, even if there are not an integral number of lamp periods per scan line integration time, the integrated irradiance signal remains the same from scan line to scan line. However, the effectiveness of phase synchronization depends on the stability of the lamp power supply in frequency or period. Any variation in the period of the lamp power supply will induce a strobing nonuniformity into the image.
The present invention contemplates a new and improved method and apparatus for eliminating lamp strobing in a scanning system, which overcomes the above-referenced problems and others.